1. Field of the Invention
The present invention relates to volumetric metering equipment, especially but not exclusively for use in metering the volume of fluid pumped through one or more injectors by a diesel-engine fuel injection pump.
2. Description of the Prior Art
In one previously proposed form of such equipment, fuel or test oil is directed from such a pump to a piston cylinder arrangement in such a manner that the displacement of the piston provides an indication of the amount of fluid delivered by the pump. When the piston reaches its extreme end of delivery, with maximum displacement, a drain valve is switched to enable fluid to be released from the piston and cylinder arrangement, and so enable the piston to return to its starting end of delivery, corresponding to zero displacement. However, before subsequent displacement of the piston, following closure of the drain valve, can be considered to reflect accurately the amount of fluid delivered by the pump, dynamic equilibrium must be attained. One of the parameters involved in such dynamic equilibrium is the pressure of the fluid delivered to the piston and cylinder arrangement. It is desirable that this should be sufficient to inhibit the formation of any voids in the fuel or test oil. Therefore, after a return of the piston to its starting end of delivery, a certain number of injections from the pump are disregarded in order to enable the system to build up the desired back pressure. This results in an undesirable loss of time in the course of a metering operation.